Adhesion between cells plays an essential role in development and maintenance of tissue form and function. Intercellular adhesion is mediated by a class of adhesive cell surface proteins commonly referred to as "cell adhesion molecules" or "CAMs". These proteins have been identified and characterized in a phylogenetically diverse range of organisms and have been found in many cases to be highly conserved in structure. Certain cell surface CAMs are members of a superfamily of glycoproteins which are structurally related to immunoglobulins, i.e., their structure contains a number of extracellular immunoglobulin-like and fibronectin Type III-like domains.
The immunoglobulin superfamily of CAMs includes the neural cell adhesion molecule (N-CAM), the L1 antigen, Ng-CAM, TAG-1, and others. These CAMs are believed to mediate homophilic binding between cells and have also recently been recognized as participants in heterophilic interactions with other cell surface molecules, extracellular matrix proteins and proteoglycans. Many are also believed to be involved in transmission of signals to the interior of the cell which modulate cell morphology, cell metabolism and cell adhesion. The means by which these molecules transmit signals to the interior of the cell is unclear.
The F11 antigen (F11) is a chicken neural cell surface-associated glycoprotein which is believed to be involved in neurite-neurite interactions. The cDNA sequence of F11 has been determined and it codes for a 1010 amino acid protein (Bruimmendorf, et al. (1989) Neuron 2:1351-1361). The F11 molecule comprises six domains related to the immunoglobulin domain type C and four domains similar to the fibronectin Type III repeat. These structures are also present in L1 and N-CAM. The cDNA sequence of F11 was found to be almost identical to the cDNA sequence of the chicken neural glycoprotein contactin (Ranscht, et al. (1988) J. Cell Biol. 107:1561-1573; Zisch, et al. (1992) J. Cell Biol. 119:203-213) and it is now believed that the molecules are the same (contactin/F11). However, prior to Applicants' invention, the identity was not clear. A mouse neural cell surface protein, F3, has been identified and is the homologue of the chicken neuronal cell adhesion protein contactin/F11. The cDNA which codes for F3 has been cloned and sequenced, revealing an open reading frame encoding a 1020 amino acid protein having the characteristics of the immunoglobulin superfamily (G. Gennarini, et al. 1989. J. Cell Biol. 109:775-788).
The present invention relates to CAMs involved in human neural cell adhesion. Specifically, the present invention provides the purification and characterization of the human counterpart of the mouse F3 and chicken contactin/F11 proteins, the preparation of monoclonal and polyclonal antibodies to the human contactin and nucleic acid sequences encoding the human contactin. E. Berglund, et al. (1987. J. Neurochem. 48:809-815) have used monoclonal antibodies to characterize glycoproteins in human brain and have reported isolation and characterization of a molecule identified as Gp135 (E. Berglund, et al. 1991. Eur. J. Biochem. 197:549-554; E. Berglund, et al. 1991. Brain Res. 549:292-296). These authors sequenced the amino terminus of the protein and an internal peptide. On the basis of these sequences they identified a similarity to chicken contactin/F11 and mouse F3, however, the reported amino acid sequence of Gp135 is different from that of the human contactin molecule described herein. It was therefore also unclear prior to Applicants' invention whether or not human Gp135 was the direct homolog of F3, contactin/F11. E. Berglund and B. Ranscht later reported the isolation and partial characterization of cDNA clones encoding Gp135 (1992. Soc. Neurosci. Abst. 18:1325, Abst. # 560.5).